I do believe the 2004 video is real. However, there are two problems here. First, a video from 2004 inherently cannot be used as a reason for why we should have invaded Afghanistan in 2001. Second, if the December 2001 video was fake, that makes any further statements from OBL very suspect even if they are authentic. That is, any later statements made be OBL should be given much less weight as evidence against him. (In fact, in any trial that was actually fair the charges would be dropped if it was in fact determined that the U.S. had falsified evidence against him.)

edit: rewritten for clarity.